1. Field of Application
The present invention relates to an electric current detection apparatus for detecting values of electric current flow in each of two systems which always have respectively different conduction occasions, where the term “conduction occasion” is used herein to signify a time during which current flow occurs through a specific electrical system or conductor.
In particular, the invention relates to such an electric current detection apparatus that is applicable to two systems having a large difference between the respective dynamic ranges of currents which flow in the two systems. The invention further relates to an electric current detection system, a battery module which combines a current detection function with a storage battery, and a battery status monitoring method, each of which utilize such an electric current detection apparatus.
2. Prior Art Technology
In recent years, with increasing amounts of electrical apparatus being mounted on motor vehicles, the requirements for the amount of electric power that must be supplied to the electrical apparatus from the electrical storage battery (referred to hereinafter simply as the battery) of the vehicle has increased accordingly. At the same time, due to the need to ensure high reliability of the electric power supply of a motor vehicle, advances have been made in technology for monitoring the status of the battery, i.e., for monitoring the SOC (state-of-charge), indicative of the degree to which the battery is charged, and the SOH (state-of-health), indicative of the overall condition of the battery and in particular the remaining energy storage capacity of the battery (referred to in the following simply as the residual capacity).
A typical method of battery status detection is described for example in Japanese Patent Laid-open No. 2910184, wherein a correlation map of the relationships between values of internal resistance of a vehicle battery and values of residual capacity of the battery is prepared and stored beforehand. When the vehicle engine is started, a residual capacity value is calculated using the correlation map, based on the internal resistance of the battery at that time. Thereafter, that residual capacity value is successively incremented or decremented in accordance with successive amounts of discharge current from the battery or of charging current supplied to the battery, to thereby successively update the actual residual capacity value.
The internal resistance of the battery at the time of engine starting is calculated based on the starting current that is supplied from the battery to the starter motor of the vehicle when the engine is being started, and the voltage that appears between the battery terminals at that time.
When a vehicle engine is started by using the starter motor, then as shown in FIG. 10A the starter signal is held at a level which will be referred to as the ON level during a time interval t1˜t2, during which a very high level of starting current (for example, 500˜1000 A) flows, for producing sufficient torque to start the engine. When engine starting has been completed, the generator of the vehicle begins to be driven by the engine to generate electric power, and this initiates charging of the battery by a flow of charging current from the generator. Rapid charging of the battery occurs while the charging current is initially at a high level during the interval from t2˜t3 as shown in FIG. 10A. However the level of charging current at that time (and thereafter) is substantially lower than the starting current, being approximately 200 A or lower.
If it is attempted to use a single magnetic sensor to measure the respective values of current that flow in such two systems during two respectively different conduction occasions (i.e., the conduction occasions from t1 to t2 and from t2 to t3, respectively), then since the currents that flow in the two systems have respective dynamic ranges that differ greatly, it is necessary to use a magnetic sensor having a detection range corresponding to the largest of the aforementioned two dynamic ranges, as illustrated in FIG. 10B. However if the detection range is made so large, then the detection resolution will become correspondingly lower, so that problems arise with respect to accuracy of detection when measuring the levels of battery current that flow after engine starting has been completed.
In the prior art, in order to accurately measure the currents which flow in two such different systems whereby the respective currents have dynamic ranges that differ greatly, it has been necessary to use two electric current detection apparatuses which have respectively different detection ranges, or (as described in Japanese Patent Laid-open No. 06-201731) to use a magnetic balance type of electric current detection apparatus that can be switched in detection range.
However if an electric current detection apparatus utilizing two current detectors having respectively different detection ranges is used, then the overall size of the apparatus will become large, so that it is difficult to find space for mounting the electric current detection apparatus in the vehicle, and in addition this is not an efficient measure, from the aspect of manufacturing costs.
On the other hand, if an electric current detection apparatus having the magnetic balance type of current detector is used, with switching of the current detection range being accomplished by varying the offset magnetic flux, it is necessary for the current detector to incorporate a feedback winding and a bias winding, wound around a magnetic core. Hence, the structure becomes complex, so that the manufacturing cost is high. Furthermore, due to the inductance of the feedback winding, the problem arises that the switching response when changing the detection range is poor.